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PREFACE TO THE EIGHTH EDITION 



AS the preface to the sixth edition of this work expresses accurately what 

 should be said to-day it is appended : 



1 'The rapid advance in microscopical knowledge, and the great strides in the sci- 

 ences employing the microscope as an indispensable tool, have reacted upon the 

 microscope itself, and never before were microscopes so excellent, convenient and 

 cheap. Indeed, the financial reason for not possessing a microscope can no longer 

 be urged by any high school or academy, or by any person whose profession de- 

 mands it. 



Naturally, to get the greatest good from instruments, tools, or machines of any 

 kind, the one who uses them must understand the principles upon which their 

 action depends, their possibilities and limitations. 



That the student may acquire a just comprehension of some of the fundamental 

 principles of the microscope, and gain a working acquaintance with it and its ap- 

 plications, this book has been prepared. It is a growth of the laboratory, and has 

 been modified from time to time to keep pace with optical improvements and ad- 

 vancing knowledge." 



In rewriting this edition the different chapters have been recast, new figures 

 added and in most cases the matter considerably increased. A new chapter has 

 been added upon class demonstrations. The general availability of the constant 

 electric current, and the improvement in apparatus have made micro-projection 

 practicable and satisfactory. It has served the writer so well in his teaching of 

 histology and embryology that it seemed worth while to give the benefit of his ex- 

 perience to his fellow workers. 



It is hoped that the book as it now stands will serve more completely than 

 ever before the needs of the class-room and of the laboratory. 



"Simply reading a work on the microscope, and looking a few times into an 

 instrument completely adjusted by another, is of very little value in giving real 

 knowledge. In order that the knowledge shall be made alive, it must become a 

 part of the student's experience by actual experiments carried out by the student 

 himself. Consequently, exercises illustrating the principles of the microscope 

 and the methods of its employment have been made an integral part of the work. 



"In considering the real greatness of the microscope, and the truly splendid 

 service it has rendered, the fact has not been lost sight of that the microscope is, 

 after all, only an aid to the eye of the observer, only a means of getting a larger 

 image on the retina than would be possible without it ; but the appreciation of 



